The software expects to communicate via a legacy (usually COM1 or COM2). If your computer only has USB ports, you will need a high-quality USB-to-Serial adapter featuring a FTDI chip . Cheaper Prolific chips often fail to maintain the strict timing required by DOS-based RSS. Step-by-Step Programming Process
You need a Motorola-compatible RIB to translate the serial data signals from the computer to the radio. motorola radius sp50 programming software.zip